Quick release safety windshield

ABSTRACT

A quick release windshield is constructed of a thin sheet of glass, an interlayer of poly-vinyl butyral and a surface layer of a cellulose aceto-butyrate or cellulose tripropionate. The cellulose ester is preferably mounted on the butyral by means of a transparent adhesion-promoter such as tin-II-chloride. For use in places where the organic layer is apt to be marred, its surface is hardened by the application of a coating of an organic polysiloxane. The glass projects beyond the organic layers and serves as the only major mounting means.

United States Patent 1 Blank 1 Oct. 2, 1973 1 1 QUICK RELEASE SAFETYWINDSHIELD [75] lnvent or: Kurt Blank, l-laselsteig, Germany [73Assignee: Saint-Cobain, Boulevard Victor Hugo Neuilly sur Seine, France[22] Filed: Mar. 15, 1971 [21] Appl. No.: 124,222

[30] Foreign Application Priority Data Mar. 16, 1970 France 7009212 [52]US. Cl ..t 161/40, 161/44, 161/145, 161/199,161/209,156/99,156/l06 [51]Int. Cl B32b 17/10, B32b 31/12 [58] Field of Search 161/199, 201, 209,161/208, 1 45,39, 44, 40; 156/308, 99, 104,

[56] References Cited UNITED STATES PATENTS 12/1971 Bruckner et al.161/199 X 10/1941 McNally 161/201 3,445,326 5/1969 Hurst 161/2082,184,876 12/1939 Shcrts 161/199 3,341,399 9/1967 Hazdra et a1. 161/1993,455,754 7/1969 Buzzell et a1. 156/99 2,047,253 7/1936 Brooks 161/201 XPrimary Examiner-Daniel J. Fri'tsch A!t0meyJohn L. Seymour and Arthur W.Dew

[57] ABSTRACT A quick release windshield is constructed of a thin sheetof glass, an interlayer of poly-vinyl butyral and a surface layer of acellulose aceto'butyrate or cellulose tripropionate. The cellulose esteris preferably mounted on the butyral by means of a transparentadhesion-promoter such as tin-ll-chloride. For use in places where theorganic layer is apt to be marred, its surface is hardened by theapplication of a coating of an organic poly siloxane. The glass projectsbeyond the organic layers and serves as the only major mounting means.

11 Claims, 4 Drawing Figures PmzmEnw'zma LNVENTOR. KURT BLANK 62 MWATTORNEYS QUICK RELEASE SAFETY WINDSI-IIELD This invention relates to awindow of novel construction which is particularly adapted to use as anautomobile windshield and which will be described in that use withoutlimiting the generality of its application. The invention is animprovement on that of United States application Ser. No. 794,152 filedJan. 27, 1969, now U.S. Pat. No. 3,630,812, issued Dec. 28, 1971 andwhich is assigned to the same assignee. The invention described in theprior application relates to a windshield which gives way readily aftershock, such as projection of a body against it during an automobileaccident, and which yields at the edges, not at the center, constitutinga material protection to occupants of the vehicle.

The accompanying drawings illustrate that prior invention and thefollowing description is taken from the prior specification:

FIG. 1 shows in section the structure of a windshield, in accordancewith the invention, constituted by a laminated sheet;

FIG. 2 represents in section a preferred mode of construction of theframe using a rubber section;

FIG. 3 represents in section another construction of the frame in thecase of a fastening of the windshield by cementing directly onto the carbody;

FIG. 4 is a partial, cross-sectional view of a windshield in accordancewith the characteristics of the invention and consisting of a singlesheet of safety glass;

As can be seen on FIGJ, the side of the novel windshield not receivingthe impact directly, i.e. the outer side, consists of a sheet ofsilicate glass 1 held along its periphery in the frame 2. Along the sidereceiving the impact there is a smaller sheet 3. The latter terminatespreferably, along its entire periphery, within the frame in which thesheet of silicate glass 1 has been fixed so that, contrary to thelatter, it is not held tightly in the frame. In accordance with a firstmode of realization,

this smaller sheet 3 is made of plastic;

The sheet of silicate glass 1 is joined to the plastic material sheet 3by means of a spacer layer 5 made of a suitable cement. This cementlayer is preferably selected in such a way that it will, within thetemperature range referred to above, absorb the mechanical tensionstresses generated as a result of the difference of thermal expansionbetween the glass and the plastic material;

Considering the minimum value, required according to the invention, ofthe mechanical properties of the substance making up the plasticmaterial sheet 3, this substance can be chosen from among the knownplastic materials. Thus, for instance, the required conditions aresatisfied in the case of an ethylene glycol polyterephthalic ester sheetof a thickness of 0.25 mm., a high molecular weight thermoplasticpolycarbonate sheet of adihydroxylated aromatic compound, in particulardiphenynolalkane, of a thickness of 1 mm., an amorphous polyamide sheetof bifunctional aromatic acids, in particular terephthalic acid and analkyl substituted bifunctional aliphatic amine, in particular diaminehexamethylene, of a thickness of 0.25 mm. or even a polyvinyl chloridesheet free of plasticizer, of a thickness of 0.5 mm.;

The sheet 3, of smaller size, can likewise be of silicate glass,provided one sees to it that the interpolated plas- 5, is endowed in itsmedian zone with the strength re quired for perforation. The sheet ofglass 1 has a thickness of 2 to 8 mm. and the sheet of glass 3 has athickness of 0.1 to 3 mm. The interpolated plastic layer 5 consists ofpolyvinyl butyral and has a thickness of at least 0.7 mm.;

FIG. 2 represents another mode of realization of the frame in which thesmaller size sheet 3 is firmly supported in order to prevent a collapseof the windshield toward the inside of the vehicle :in the event of thebreaking of the outer sheet of glass 1 under the effect of an impactcoming from outside. To this end, the part 10 of the car bodyconstituting the frame of the windshield is extending in order that theupper part 11 of its frame overlap the periphery of the sheet 3. Therubber section 12 has, in this area, been widened by the lip 13 whichapplies against the sheet 3. In this case, of course, care must beexercised in order that there should not be any adhesion between theperiphery of the sheet 3 and the lip 13 of the rubber section so that,in the event of an accident, the sheet 3 can easily liberate itself fromthe rubber section, and move outward or forwardly;

If the use of a rubber section is dispensed with, the frame can suitablybe executed on the car body, as shown in FIG. 3. In this case, therabbet of the frame 20 is bent twice in stepwise fashion so that theouter sheet of glass 21 and the inner sheet of glass 23 are hemmed in bythe steps formed in this manner. The outer sheet 21 is fixedly attachedto the car body 20 along its entire periphery by means of a suitablecement 24. The inner sheet 23, on the contrary, must not be connected tothe car body in any way. To this end, one can interpose between theperiphery of the sheet 23 and the corresponding part 25 of the frame asuitable separating means 26;

FIG. 4 illustrates a mode of realization of a windshield in accordancewith the invention, made of a single pane of safety glass. In the caseof these windshields, the median area 30 consists of a silicate glasshaving a flexural strength of at least 50 kgf./mm. and preferablybetween 50 to I00 kglf./mm. The peripheral zone 31 has, on the contrary,a flexural strength of 20 kgf./mm. at the most. The peripheral zone 31is cemented onto the sheet metal 33 of the car body by means of a cementlayer 32. The upper portion 35 forming the rabbet of the sheet-metal 33,which extends to face the peripheral zone 32 and which overlaps up tothe median zone 30 ,of the sheet of glass in order to protect it fromcollapsing toward the inside, is not cemented to this sheet either. Thisholds likewise with regard to the upper portion 36 of the part of therubber section situated on the inner side.

It will be perceived that the patent above identified relates to asafety windshield constituted of two elementary sheets of glass with aninterlayer of plastic, usually polyvinyl butyral, which is weakened atits periphery so that under shock the median part is projected forwardas a unit while the weak peripheral zone breaks to release it. In thatwindshield the exterior layer is silicate glass and the interlayer andinner layer have smaller dimensions than the layer which is fixed in theframe. Most of the interlayer and inner layer are not gripped by theframe. The plastic interlayer and the inner layer have such strengththat they are not perforated by a spherical body weighing20 kg. strikingwith an impact to 50 km./hr

The prior application includes layered Windshields in which the interiorlayer may be plastic, preferably thermoplastic, and which has atemperature acceptance between 20C. and +40C., a resistance to ruptureof at least 5 kg-cm/cm, and a resistance to traction above 200 kg./cm.(0.1 percent elastic limit).

It has now been discovered by the present inventor that superiorWindshields of the foregoing type are made when the innermost layer ofthe sandwich is com posed of cellulose-acetobutyrate or of cellulosetripropionate. Such novel Windshields give superior results and superiorprotection in case of accident, particularly when the windshieldincludes an outer layer of silicate glass (silia-soda-lime glass forinstance) when the cellulose ester has a thickness from about 0.2 to 0.5mm., and when the plastic interlayer is composed of polyvinyl butyralhaving a thickness above about 0.7

It is my discovery that polyvinyl butyral does not adhere well toplastics but that cellulose esters, particularly celluloseaceto-butyrate, can be made to adhere firmly and permanently to thebutyral, especially when adhesion is secured by means hereinafter to bedescribed. An advantage of this novel windshield is that only a verythin layer of the cellulose ester need be used with the polyvinylbutyral. This produces the additional advantage that Windshieldscomprising the very thin films of this invention are optically superiorto windshields embodying the thicker sheets required by the use of othermaterials. These thin cellulosic sheets also import yet anotheradvantage that they are very flexible, tend to flex rather than torupture, and contribute much to the great resistance to perforationwhich is possessed by the polyvinyl butyral.

Among the cellulose esters which are suited to this use, the clarity,optical superiority and physical characteristics of celluloseaceto-butyrate make it preferred as the outer plastic layer of the threemain layers of the sandwich; it has superior thermoplastic propertiesand superior mechanical resistance at low temperatures, e.g. those wellbelow zero. It also has the excellent characteristic that itsthermoplastic properties can be altered materially by the choice andconcentration of the plasticizer which is incorporated within it, makingit possible to vary its qualities for particular uses. Cellulosetripropionate is also useful but not equal in most uses to theaceto-butyrate.

The aceto-butyrate is like many plastics in being subject to scratchingby abrasion and it is a part of this invention to prevent such damage.This is accomplished by applying a coating of an organo-polysiloxane tothe exposed face of the plastic. These compositions are found onthemarket and can be used as a coating composition in aqueous oralcoholic solution. For instance, methyltrialkoxysilane is heated inwater until it has formed a partial condensation product, then at ahigher temperature, up to 300C, to remove lay-products, and finallybelow the gel point to produce the solvent soluble organo-polysiloxanewhich is applied to the cellulose aceto-butyrate sheet and cured. Whenapplied and dried their optical properties are excellent and theyincrease the resistance of the cellulose ester to marring on the orderof 5 to times.

Because of their thermoplastic nature the cellulose ester and polyvinylbutyral interlayer can be welded together by heat and pressure but asuperior bond is produced if adhesion A is secured by the use of asolution in alcohol of tin chloride. or an aminosilane. or

an epoxy silane, for instance Union Carbides A 1100(gammaaminopropy1triethoxysilane) or A187(gamma-g1ycidoxypropyltrimethoxysilane). A solution of 1 to 8 percent ofstannous chloride. SnCl in ethyl alcohol is sprayed on the sheet ofcellulose aceto-butyrate which is immediately applied to the polyvinylbutyral.

EXAMPLE 1 A sheet of silica-soda-lime glass of a type ordinarilyemployed in the manufacture of Windshields, having a thickness of 2-3mm. was bent by ordinary bending machinery with the double curvaturetypical of the modern windshield. To this a sheet of polyvinyl butyral0.76 mm. thick was attached thermally in a known manner. A solution oftin chloride in alcohol was used to wet the face of the polyvinylbutyral and a sheet of cellulose acetobutyrate was applied thereover andsqueegeed into bubble-free adherence. The dimensions of the glass faceof the sandwich allowed the edges of the glass layer to project beyondthe organic layers sufficiently to be mounted in the windshield frame,as described hereinabove.

EXAMPLE 2 A preferred method of joining the parts of the windshield isto enclose the parts, the glass and organic layers and the adhesivesduly and correctly assembled and aligned within a plastic sack, and toevacuate the sack while applying air pressure to the outside of the sackat a temperature suited to the operation. Such a process is recited indetail in the application for patent identified as Oustin and Krumm,Ser. No. 10,911, filed Feb. 12, 1970, which is assigned to thisassignee. This will, in many cases, involve an initial temperature ofC., 4 to 10 atmospheres pressure, the progressive reduction oftemperature to 50C., and a final chill to room temperature. In thepresent invention it is advisable to adopt the additional step ofapplying a glass pressure plate having the same curvature as the finalarticle over the outer plastic layer of the sandwich, to be removedafter the joining of the layers has been completed. The product of thisprocess is superior in function and superior in optical properties toprior products adapted to such use.

It is sometimes useful to attach the two organic layers one to the otherbefore applying them to the layer of glass or to assemble the parts oneby one but the preferred process is as stated in Example 2. In thepreferred form of the invention the cellulosic layer will then receive acoating of an organo polysiloxane to protect its surface againstabrasion, or the protective layer can be applied before the organiclayers are mounted on the glass. The preferred form of the inventionwill thus have five layers-the glass, the polyvinyl butyral, theadhesive, the cellulose ester, and the siloxane. In cases where thesandwich is not liable to be scratched the siloxane may be omitted. incases where maximum adhesion is not necessary the layer of internaladhesive may be omitted. 1

Another process for assembling the windshield takes into considerationthe thickness and small rigidity of the cellulose aceto-butyrate, whichis applied to a sheet of glass of suitable curvature, or to a preformedplastic plate (e.g. 2 mm. thick) of any suitable transparent plastic,for instance another sheet of polyvinyl butyral. A suitable temperaturefor attaching the organic layers one to the other is 135C. In general,the mounting of a sheet of plastic on bent glass (e.g. on a glass sheetof double curvature, that is to say a curvature about more than one axisproducing the so-called wraparound windshield) is not difficult, thesheet of cellulose acetobutyrate being sufficiently plastic and bendableat this temperature to accommodate itself to the curvature of the glasswithout difficulty, if the curvature about one of the two axes does notexceed a certain limit.

The Windshields of this novel construction comply with the legalrequirements for safety glass, their resistance to perforation isextremely high and they break off at the edges upon the application ofrelatively slight impact against the plastic side. The thin plastic istough, resists penetration by glass shards, and protects the head of aperson projected against the windshield against cutting even when theglass breaks. The forces of reaction which cause such damage to thehuman organism when prior safety glass is used are minimized, and evenwhen the layers involve one of glass and two of plastic, for instance awindshield having an outer sheet of glass 3 mm. thick, and an outersheet of transparent polyamide 1 mm. thick sandwiched by polyvinylbutyral 0.76 mm. thick, the forces of reaction are reduced by one half.There are other advantages such as reduction by weight and improvementof optical qualities.

As many apparently widely different embodiments of the present inventionmay be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments.

What is claimed is:

l. A windshield consisting essentially of a glass sheet, an interlayerof polyvinyl butyral adhered to one surface of the glass sheet, and acellulose ester layer selected from the group consisting of celluloseacetobutyrate, cellulose aceto-propionate-and cellulose tripropionateadhered to and over the other surface of the polyvinyl butyralinterlayer.

2. A windshield according to claim 1, and a coating oforgano-polysiloxane on the otherwise exposed surface of the celluloseester layer.

3. A windshield according to claim 1 in which the polyvinyl butyral andcellulose ester layers have dimensions which leave a rim of the glasssheet projecting beyond their edges.

4. A windshield according to claim 3 in which the layer of celluloseester is about 0.2 to about 0.5 mm. thick and the polyvinyl butyrallayer has a minimum thickness of about 0.7 mm.

5. A windshield which consists essentially of an exterior first layer ofglass, a transparent cellulosic ester second layer selected from thegroup consisting of cellulose aceto-butyrate, cellulose aceto-propionateand cellulose tripropionate and a third layer of polyvinyl butyralinterposed between and adhered to said first and second layers, saidsecond and third layers being superposed and essentially covering onesurface of said first layer.

6. A windshield according to claim 5 in which said glass layer projectsa limited distance beyond the periphery of said second and third layers,and a mounting frame surrounding the windshield and attached essentiallysolely to the projecting portion of said glass layer.

7. A windshield according to claim 5 in which said second and thirdlayers are adhered by means of a solution in alcohol of an adhesionpromoter selected from tin chloride, gamma-aminopropyltriethoxysilaneand gamma-glycidoxypropyltrimethoxysilane applied to at least one of theinterfaces of said second and third layers.

8. The method of adhesively joining the organic layers of a laminatedwindshield comprising a first outer layer of glass, an interlayer ofpolyvinyl butyral, and a second outer layer selected from the groupconsisting of cellulose aceto-butyrate, cellulose aceto-propionate andcellulose tripropionate, which comprises coating with an alcoholicsolution of one of the substances selected from the group oftin-lI-chloride, gammaaminopropyltriethoxysilane andgammaglycidoxypropyltrimethoxysilane at least one of the interfacesbetween the interlayer and the second layer, and heating and pressingtogether the interfaces.

9. The method of claim 8, and coating the exposed face of the secondouter layer with an organo polysiloxane.

10. A method of making a safety windshield which comprises, adhesivelyconnecting in superposed relation an interlayer of polyvinyl butyral, afirst outer layer of glass and a second outer layer selected from thewith an adhesion promotor selected from the group consisting of tinchloride, gamma-aminopropyltriethoxysilane andgamma-glycidoxypropyltrimethoxysilane.

1 l. A method according to claim 10 having the added step of coating theouter face of the second outer layer with an organo polysiloxane. a:

2. A windshield according to claim 1, and a coating oforgano-polysiloxane on the otherwise exposed surface of the celluloseester layer.
 3. A windshield according to claim 1 in which the polyvinylbutyral and cellulose ester layers have dimensions which leave a rim ofthe glass sheet projecting beyond their edges.
 4. A windshield accordingto claim 3 in which the layer of cellulose ester is about 0.2 to about0.5 mm. thick and the polyvinyl butyral layer has a minimum thickness ofabout 0.7 mm.
 5. A windshield which consists essentially of an exteriorfirst layer of glass, a transparent cellulosic ester second layerselected from the group consisting of cellulose aceto-butyrate,cellulose aceto-propionate and cellulose tripropionate and a third layerof polyvinyl butyral interposed between and adhered to said first andsecond layers, said second and third layers being superposed andessentially covering one surface of said first layer.
 6. A windshieldaccording to claim 5 in which said glass layer projects a limiteddistance beyond the periphery of said second and third layers, and amounting frame surrounding the windshield and attached essentiallysolely to the projecting portion of said glass layer.
 7. A windshieldaccording to claim 5 in which said second and third layers are adheredby means of a solution in alcohol of an adhesion promoter selected fromtin chloride, gamma-aminopropyltriethoxysilane andgamma-glycidoxypropyltrimethoxysilane applied to at least one of theinterfaces of said second and third layers.
 8. The method of adhesivelyjoining the organic layers of a laminated windshield comprising a firstouter layer of glass, an interlayer of polyvinyl butyral, and a secondouter layer selected from the group consisting of celluloseaceto-butyrate, cellulose aceto-propionate and cellulose tripropionate,which comprises coating with an alcoholic solution of one of thesubstances selected from the group of tin-II-chloride,gamma-aminopropyltriethoxysilane andgamma-glycidoxypropyltrimethoxysilane at least one of the interfacesbetween the interlayer and the second layer, and heating and pressingtogether the interfaces.
 9. The method of claim 8, and coating theexposed face of the second outer layer with an organo polysiloxane. 10.A method of making a safety windshield which comprises, adhesivelyconnecting in superposed relation an interlayer of polyvinyl butyral, afirst outer layer of glass and a second outer layer selected from thegroup consisting of cellulose acetO-butyrate, cellulose aceto-propionateand cellulose tripropionate, the interlayer and second layer havingperipheral dimensions less than those of the first layer, therebyproviding a projecting rim of uncovered glass for attachment to amounting frame, and coating the interfaces of the cellulosic secondlayer and the polyvinyl butyral interlayer with an adhesion promotorselected from the group consisting of tin chloride,gamma-aminopropyltriethoxysilane andgamma-glycidoxypropyltrimethoxysilane.
 11. A method according to claim10 having the added step of coating the outer face of the second outerlayer with an organo polysiloxane.